1. Field of the Invention
The present invention relates to an ASK(Amplitude Shift Keyed) receiver, and more particularly, to an ASK receiver using a digital circuit.
2. Discussion of the Related Art
An ASK technique is a modulation technique used in communication technology. For digital signals such as `0` and `1`, one signal is carried with a frequency and the other is carried without a frequency as shown in FIG. 1. A conventional ASK receiver will be explained with reference to FIG. 2.
As shown in FIG. 2, a conventional ASK receiver includes a pre-amplifying part 1 for amplifying an amplitude shift keyed and received signal, a band pass filter 2 for passing a signal only within a predetermined band of the signals from the pre-amplifying part 1, a detector 3 for obtaining an original low frequency signal from an output of the band pass filter 2, a delaying part 4 for delaying a signal from the detector 3 for a predetermined period of time, a signal stretcher 5 for stretching a signal from the detector 3 using a capacitor, a dynamic threshold generator 6 for generating a threshold value for determining whether the received signal exceeds a noise level, and a microprocessor 7.
The operation of the conventional ASK receiver having the aforementioned system will now be explained. Referring to FIG. 2, in order to obtain a signal only within a predetermined band, an amplitude shift keyed and received signal is amplified through the pre-amplifying part 1 and filtered by the band pass filter 2. The filtered signal is received at the detector 3. The detector 3 generates a high bit level pulse if a carrier signal is present and produces a low bit level pulse if no carrier signal is detected. Then, the output signal from the above detector 3 is inputted to the delaying part 4, the signal stretcher 5, and the dynamic threshold generator 6, respectively. The delaying part 4 delays the signal generated from the detector 3 for a predetermined period of time, and the signal stretcher 5 stretches the signal using a capacitor. The dynamic threshold generator 6 produces a threshold value for determining whether a received signal exceeds a noise level. Those signals from the detector 3 delayed for a predetermined period of time by the delaying part 4 that are greater than the threshold value generated from the threshold generator 6 and at the same time have a section greater than the signal stretched in the signal stretcher 5 are produced as a high bit digital signal. The signals in the remaining sections are produced as low bit digital signals. Finally, the outputted values are transmitted to the microprocessor 7 and converted to binary digit signals.
However, the conventional ASK receiver has the following problems. First, the conventional ASK receiver uses an analog signal system which has low reliability and high power consumption. Second, realization of a highly integrated device with other digital circuits is difficult, and a separate analog power source generates high noise level.